One can read more here. Do the following hadiths justify these executions?1) Abu Ya’la narrated in his Musnad from Ibn ‘Abbaas (may Allaah be pleased with him) that the Prophet (peace and blessings of Allaah be upon him) said: “The bonds of Islam and the bases of religion are three, on which Islam was founded. Whoever gives up one of them becomes a kafirthereby andit is permissible to shed his blood: the testimony that there is no god but Allaah, the prescribed prayers and fasting Ramadan.”

2} Narrated Ikrima, "Some atheists were brought to Ali and he burnt them. The news of this event, reached Ibn Abbas who said, "If I had been in his place, I would not have burnt them, as Allah's messenger forbade it, saying, "Do not punish anybody with Allah's punishment (fire)." I would have killed them according to the statement of Allah's Messenger, "Whoever changed his Islamic religion, then kill him." [Sahih Bukhari 9:57]

Muhammad is considered the role model for Muslims -- "Certainly you have in the Messenger of Allah an excellent exemplar for him who hopes in Allah and the latter day and remembers Allah much." (Quran 33:21). So did Muhammad always ensure that captive women were treated in an exemplary way?Consider the following hadith:"We [Muhammad’s merry men] went out with Allah's messenger on the expedition to the Mustaliq and took captive some excellent Arab women; and we desired them for we were suffering from the absence of our wives, (but at the same time) we also desired ransom for them. So we decided to have sexual intercourse with them but by observing azl" (withdrawing the male sexual organ before emission of semen to avoid conception). But we said: "We are doing an act whereas Allah's messenger [i.e., Muhammad] is amongst us; why not ask him?" So we asked Allah's messenger and he said: "It does not matter if you do not do it, for every soul that is to be born up to the Day of Resurrection will be born". (Sahih Muslim, Vol. 2, #3371)Tellingly, the role model of the Muslims, Muhammad, does not exclaim:“DO NOT FORNICATE WITH THE CAPTIVES!”

Nor does he exclaim to the married men: “DO NOT COMMIT ADULTERY WITH THE CAPTIVES!!”

Finally, we note that he does not yell: “DO NOT RAPE THE CAPTIVES!!!”So given that the role model of the Muslims, Muhammad, had no problem with female captives being raped, can we truly be surprised that the Islamic State has no problem with the rape of captives either?